The replacement of chlorofluorocarbons (CFC's) widely used in refrigerant compositions, propellants and cooling fluids as well as blowing agents, solvents and rinse agents with environmentally acceptable alternatives has produced an abundance of compounds meeting one or more of these needs. The most acceptable replacement compounds are those having little or no chlorine, since it is generally accepted that chlorinated aliphatics lead to unacceptable reactive chlorine-containing radicals when present in the upper atmosphere. These radicals are thought to react with the ozone in the stratosphere depleting it to dangerously low levels.
One of the more promising alternatives to CFC's are the aliphatic compounds where chlorine has been partially or completely replaced with fluorine. These materials are known respectively as hydrochlorofluorocarbons (HCFC's) and hydrofluorocarbons (HFC's). Typical HCFC's and HFC's have atmospheric lifetimes and global warming potentials that are a fraction of their fully chlorinated analogs. However, many of their other physical properties (low flammability and toxicity, sufficient volatility, etc.) are identical or similar to the CFC's. Accordingly, they are attractive replacements for the chlorinated molecules.
In processes for preparing HCFC's and HFC's, a usual starting material is the chlorinated analog of the desired fluorinated compound. Thus, U.S. Pat. No. 2,787,646 discloses that SbF.sub.3 Cl.sub.2 and SbF.sub.3 are useful for converting compounds of the formula CMZ.sub.2 CX.dbd.CHY, for example 3,3,3-trichloroprop-1-ene or 1,1,3-trichloroprop-1-ene to compounds of the formula CF.sub.3 CX.dbd.CHY, for example 3,3,3-trifluoroprop-1-ene.
The preparation of 1-chloro-1,1,3,3,3-pentafluoropropane and of 1,1,1,3,3,3-hexafluoropropane from 1,1,1,3,3,3-hexachloro-propane in the liquid phase is described in EPO Publication No. 0 522 639 A1. While the preferred catalyst for the reaction is noted to be SbCl.sub.5, other catalysts disclosed are those metal chlorides, fluorides, and chloride fluorides of Group IIIa, IVa, IVb, Va, Vb and VIb of The Periodic Table of the Elements.
The processes disclosed above are illustrative of reactions that generate mixtures of hydrogen fluoride and fluorinated organic hydrocarbons. Also present in such mixture are organic by-products, hydrogen chloride, unreacted starting materials and the like. The most commonly practiced separation process for such a mixture is distillation, which facilitates the recovery of hydrogen fluoride for recycle. Unfortunately, the organic fraction that is recovered in these distillation processes also contains residual hydrogen fluoride, especially in cases where hydrogen fluoride/fluorinated organic hydrocarbon constant boiling mixtures occur. Typically, the residual hydrogen fluoride is removed by scrubbing with water and/or alkali. The process is expensive and time consuming generating wastes that require disposal and diminishing the yield of recovered hydrogen fluoride.
Unexamined Japanese Patent Application No. 56226-1996, filed Mar. 13, 1996, incorporated herein by reference, discloses a method for separating hydrogen fluoride from hydrogen fluoride mixtures with 1,1,1,3,3-pentafluoropropane by adding to such mixtures an aromatic compound such as benzene, toluene or trifluoromethylbenzene.
A method of recovering hydrogen fluoride from the above mixtures has been described in our patent U.S. Pat. No. 5,684,219, where an organic or inorganic salt is added to a mixture containing certain fluorinated propanes and hydrogen fluoride.
Other similar methods are disclosed in U.S. Pat. No. 5,632,966 and WO 97/13719.